The packages are manufactured from endless sheets by deep-drawing. Depending on the purpose for use of the packages, they consist, for example, alone of the deep-drawn lower sheet, which is closed off by the nondeformed upper sheet. However, it is also conceivable to deep-draw both the lower sheet and also the upper sheet to form a package. The packages are manufactured from the endless sheet at a deep-drawing station, in which at least several packages can be manufactured during one sequence of operation. These are still connected by the sheet. The thus formed packages are then transported by a stepwise forward movement of the sheet to a vacuum chamber, in which they are evacuated and closed off by the upper sheet. The deep-drawing station and the vacuum chamber are spaced a certain distance from one another, so that the goods can be placed into the packages formed in the lower sheet.
The sheets are gradually moved forwardly, namely in stepped increments at a rate corresponding to the rate that the already manufactured packages are being guided out of the deep-drawing station. The distance of the deep-drawing station from the vacuum chamber amounts generally to approximately 10 steps. The vacuum chamber must thus be spaced a very certain distance from the deep-drawing station and the step-by-step advance of the sheet must be carried out in exactly equal steps. If, for example, the respective steps differ only by some millimeters from the prescribed nominal value, the difference caused by this amounts at the level of vacuum chamber after 10 steps already to about 10 millimeters. The consequence is that the packages are no longer exactly guided into the vacuum chamber and during the driving together of the two halves of the vacuum chamber, the packages can be crushed and welding occurs at incorrect locations. The exact step-by-step advance of the sheets causes difficulties because, among other reasons, the sheet which is driven by the chains expands and thus the chain advance does not always correspond with the sheet advance.
Further, and in order to avoid too much stress of the foil and an overflowing of the goods from the packages, the sheet must slowly start to drive and slowly stop at each steplike advance. These requirements are not met satisfactorily with the known packaging machines.
The basic purpose of the invention is to construct a packaging machine of the above-mentioned type wherein the step-by-step advance of the sheets can be adjusted and precisely maintained, wherein the advancing speed has an approximately sinusoidal form and wherein the control device of the packaging machine is inexpensive to manufacture.
This purpose is attained inventively by providing a measuring wheel of a certain circumference to determine the magnitude of the advance of the sheets, which measuring wheel has a trip cam and by coupling with said measuring wheel a cam or impulse disk, with which the speed of the motor is controlled in dependency of the advance movement. When the measuring wheel is driven directly by the sheet, only the effective advance of the sheet is measured, so that possibly occurring expansions of the sheet may remain unconsidered. The cam disk is, according to a further suggestion of the invention, scanned by a potentiometer of a speed governor. The cam disk may be of any desired shape, so that the form or pattern of the speed during one step can be adjusted to the goods which must be transported and to the condition of the sheet.
The step length is changed inventively by changing the diameter of the measuring wheel.